Vibrating screen



June' 26, 1923.

B. A. MITCHELL VIBRATING SCREEN Filed Dec. 22, 1919- 4 Sheets-Sheet lJune 26, 1923.

B. A. MITCHELL VIBRATING SCREEN' Filed Dec. 22 1919 4 SheetsSheet 2AJune 26. 1923. 1.459.844

B. A. MITCHELL VIBRATING SCREEN Filed Dec. 22, 1919 4 Sheets-Sheet 3ATTORNEYS June 26, 1923 B. A. MITCHELL VIBRATING SCREEN Filed D60. 22,1919 4 Sheets-Sheet 4 Patented June 26, 1923.

UNITED STATES BENJAMIN A. MITCHELL, OF GARFIELD, UTAH.

VIBRA'IING SCREEN.

Application filed December 22, 1919. Serial No. 346,751.

To all 'whom t may concern.'

Be it known that I, BENJAMIN A. MITCH- ELL, a citizen of the UnitedStates, residing at G-arield, in the county of Salt Lake and State ofUtah, have invented certain new and useful Improvements in VibratingScreens, of which the following is a speciiication.

This invention relates to screening appa-.

ratus for screening crushed ore, coal, or other loose materials withwhich the machine is adapted to be used.

The purpose of the invention is to provide an improved screeningapparatus involving a new method of screening, whereby minute andsubstantially circular vibrations are set up in the screening medium,such as the ordinary wove-n wire screen cloth. The apparatus comprises asupport-ing frame, on

which the screen cloth is mounted, in combination with improvedadjusting means for setting up a high degree of tension in the screencloth. Vibrations are produced in the screen cloth by means of a rotaryvibrator embodying one or more unbalanced rotary elements which set upsubstantially circular vibrations in the vibrator casing. Thesevibrations are imparted directly to the screen cloth by rigidtransmitting elements, thereby causing each particle of the screen clothto travel in a substantially-circular path of vibration perpendicular tothe plane of the screen. An important feature of the invention is theprovision of an improved supporting frame and an improved method ot'mounting the vibrator, the frame com` prising cnd plates between whichthe screen cloth is mounted, and the underlying supporting memberconnecting the end plates and having the vibrator mounted in iiXedposition thereon. This frame is capable of angular adjustment, in ordertoregulate the flow by gravity of the loose materials thereover, and thescreen cloth can be readily detached from the frame to permitreplacement thereof when worn without interfering with the vibrating andtransmitting mechanism. Other objects of the invention relate to variousfeatures of construction, operation, and arrangement which will` bepointed out more fully hereinafter.

The nature of the invention will be understood from the followingspecification, taken in connection with the accompanying drawings, inwhich one embodiment is illustrated.

In the drawings- Figure l shows a perspective view of the frame, screencloth, and vibrator, looking toward the upper 'side thereof;

Fig. 2 is a perspective view of the apparatus illustrated in Fig. 1,looking toward the underside thereof, and illustrating the method ofmounting the vibrator on the frame; v

F ig. 43 shows an end elevation vof the screening mechanism, showing themethod of mounting the same in position to receive the loose materialsfrom a feeding hopper;

Fig. 4 is an enlarged sectional view through one of the clamping rodsand tubes at one end of the screen cloth, showing one means ofconnecting the screen cloth to the frame and adjusting the tensionthereof;

Fig. 5 is an enlarged sectional view, taken in a vertical plane parallelto the path of travel of the materials over the screen, showing somewhatdiagrammatically the character of the vibrations set up in the particlesof the screen;

Fig. 6 is a longitudinal sectional view, taken on the line 6 6 of Fig.3;

Fig. 7 shows an end elevation of one of the plates by which thevibrations are transmitted to the screen cloth;

Fig. 8 shows a longitudinal sectional view through the rotary vibrator;and

Fig. 9 shows a sectional view, taken on the line 9-9 of Fig. 8.

The supporting frame 10 in the screening apparatus comprises alongitudinal supporting base member 11 which connects in an integralmanner the upstanding end members 12, shown as curving upwardlytherefrom. The members 12 are increased in width as their upper edgesare approached, and terminate in plates 13 having side plates 14extending upwardly therefrom flush with the outer surfaces of theportions 12, thus giving the end walls of the frame an angular crosssection. The end plates are provided at their upper ends withlongitudinally projecting trunnions 15, which are adapt-ed to engage thebearing notches 16 in the brackets 17, secured tothe supporting wall 18.The lower extremities of the end plates 14 are formed integrally withhubs or bosses 20, which are provided with threaded apand of the screencarried thereby in order to secure the desired rate of flow thereover bygravity of the loose materials being screened. The loose materials aredischarged onto the upper part of the screening medium from a Lledge orplate28, which is mounted on the upper part of the wall '18 andterminates along a line parallel to the upper edge of the screen cloth.A plate 29 extends upwardly lfrom the rear edge ofthe plate 28, thusforming an intermediate receptacle adapted `to receive crushed ore orother loose materials from a hopper 80, which is mounted above theplate28 and adapted to discharge the loose materials onto a rotaryfeeding member 3l, which rotates with a shaft 32 and is adapted todischarge the loose materials over the edge of the plate onto thescreen,

The screening medium consists of a woven` wire screen cloth formed,preferably, in two sections 5L and 35, which join along a line 36 midwaybetween the upper and lower edges of the screen. The two sec tions 35aand 35T are relatively inclined, the lower section having a lesserinclination to the horizont-al than the upper section, so that thematerials passing downwardly by gravity are retarded asA they approachthe discharge edge of the screen The sections of screen cloth aresecured to the frame by means of tubes 37 and rods 38. are considerablylarger in diameter than the rods, and are provided with longitudinalslots 37a.y through which the screen cloth extends. the rod 38, and thefree end thereof carried out again through the slot, so that when a pullis exerted on the tube 37 the edges of the slot exert a snubbing actionon the screen cloth and force it against the rod 38, thus securelygripping the screen cloth between the tube and the rod.. as shown at539. The screen cloth is preferably so arranged that certain parallelstrands thereof will. extend longitudinally of the screen, while theother strands extend transversely thereto and parallel to the end platesla. The slotted tubes 37 are formed integrally with or secured to boltsor studs 40, which are adapted to engage and project through slots al.extending downwardly from the upper edges of the end plates 14. Washersl2 engage the projecting ends of the bolts and overlap the These tubesThe screen cloth is wound around walls of the slots 4l, and the nuts 43,engaging the bolts and seating against the washers, which are capable ofadjustment in order to adjust the tension of the screen 1ongitudinallythereof.

It will. be observed that the end walls of the frame are somewhatangular in shape transversely to the connecting member 11 therebyconforming to the relative inclination of the complementary sections ofthe screen cloth. lf desired, baille plates nl5 may be mounted at theends of the screen cloth to prevent loose materials from passing overthetubes 37 at the ends of the screen. These ballles may be mounted inany desired manner, but are preferably provided within-- turned loweredges, which enter the slots 37 in the tubes and are gripped between therods 38 of the` walls of the slots.

The vibrator 50, utilizes the principle of rotating moments as setvforth in my c0- pending application, Serial No. 275,32l, in producingvibration lt is arranged to be actuated internally and is mounted on theconnecting member ll midway between the ends of the supportingframe, andis housed in a casing 5l, which is formed in two parts., each -partincluding an enlarged central p0rtion 5l, of comparatively largediameter, and a smaller end portion 51h, of small dianieter. wall 52which connects it with the reduced part 51h, and each part 51b 'has anend wall 53 which is spaced inwardly from the end thereof, leaving acircular depression 54. The two parts of the casing 51 are securedtogether by means of a series of bolts 55., which extend throughapertures in the end walls 52 located just inwardly from the outercylindrical walls of the parts 51a.' These bolts are engaged at theirends by washers 56 and 57, by which the two parts of the casing aresecurely clamped together. On its lower side the casing is provided, onthe meeting line of the two parts of the casing,.

with an apertured boss having a bearing collar 58 mounted therein. Theannular beveled surface of this bearing collar adapted to coact with asimilar beveled surface formed on a supporting collar 59, which isadapted to rest upon and be secured to the connecting .member ll of theframe. A strap .60 extends around the vibrator 50 above the collar 59,and the threaded ends of this strap extend through ears ll on the sidesof the 'frame member' ll, `thus securely clamping the central part ofthe casing in position on the frame. For purposes of ventilation theconnecting member is provided with an aperture 6l. extending inwardly,Yfrom one end thereof, and this aperture communicates with the opening 62formed through the collars 58 and 59, so that air can flow or be forcedinto the interior of the cen-- trally enlarged portion of the casing.

YFlach central portion has anend lllll lll!) The air introduced into thecasing is for the purpose of cooling an electric motor, which comprisesa iield winding 6a mounted in an annular metallic casing 65, which, withthe casing 5l, serves as the field trame oi? the motor. The armature 66of the motor is mounted within the ield winding 64 on a shaft 67 whichextends longitudinally between the end walls 53. rlhis shaft isjournaled in bearing casings 7 0, which comprise enlarged parts 70alocated in the parts 5la of .the casing, and the reduced parts 70blocated in the end portions 5lb of the casing. The annular walls 7l ofthe part 70il interlockwith the frame member 65 ot' the motor, as shownat 72, and are provided with apertures 73, through which the airadmitted through the aperture 6l is permitted to pass to the motor fromthe spaces around the bolts 55. The end portion 70b of each bearingcasing is provided with a part at its end which closely iits the annularwall oiz the end portion of the casing 5l, and the end walls of thevbearing casings are provided with bearings 76 and 77, in which the shaft67 is journaled. The reduced part 70b of each end casing is hollowed outbetween the end walls thereof to form cavities 78 adapted to receivelubricating` oil, which may be inserted through the apertures, which arenormally closedfby studs 79 adapted to prevent relative rotation of thebearing casing with respect to the casing 51. The end portions 67a ofthe shaft project through the bearing casing 70 and are adapted tocarrycages 80, which, with the spherical balls 81,

`form the unbalanced elements by which cir* cular vibrations areimparted to the free ends of the casing. Each cage is provided onopposite sides thereof with a row of recesses 82, of circular crosssection and conical formation, these recesses being adapted toreceivethe balls 8l. The balls are located in one series r`of recessesonly in each cage, leaving the recesses on the diametrically oppositeside of the shatvaca-nt. The balls are carried around by the cage duringthe retation of the shaft, and are adapted to travel on independentraceways 83, which are arranged side by side between the bearing casingand the end Wall of the vibrator casing, and which are secured to thevibrator casing to prevent rotation thereof. These raceways are hollowedout annularly on their inner sides, as shown at 83a, and the ballstravell in these hollowed outl portions during the rotation of the cage.Since the balls are located 'only on one side ot the shaft, the rotationof the cage produces an unbalancing` effect by reason of the centrifugalaction or' theballs, so that substantially circular vibrations are setup in the casing.

The vibrations so set up in the casing are transmitted to the screencloth by means ot a pair ot transmitting plates 85. These plates arerelatively wideA at their central. portions and taper toward their ends,and the enlarged central portions are provided with apertures 85a whichare adapted to cngage the extremities S6 oi the casing These extremitiesare tapered on their outer suriaces to lit the corresiionding taperedapertures 85a, and after the plates have been driven to position on thecasing they are secured thereon by means of transverse tapered keys 87,which engage oppositely dis posed apertures in the parts 86. The platesare thus mounted rigidly with respect to the free ends ot` the vibratorcasing, and they extend upwardly therefrom in planes normal to theplanes ot' the screen sections and transverse to the direction in whichtension is applied in the screen, and engage the under surfaces or' thewoven wire screen 35. rlhe plates 85, which are of metal, are preterablyprovided along their upper edges with wooden transmitting members 88,which are somewhat wider than the plates 85 and which bear directly onthe under surfaces of the screen sections. The upper edG'es or' theplates are somewhat angular in contour, so that the wooden transmitting'members 88 on each plate have an angular inclination corresponding tothe relative inclination of the two sections 35 and b ci the screen.

The cages 80, which are mounted in opposite ends of the vibrator casing,are preterably mounted in the same plane,-and the balls Si in one cageare preterably mounted diametrically opposite the balls 8l in the othercage. Since the central part oi" the vibrator casing is substantiallyfixed with respect to the r'rame and the projecting ends through itvibrate, the rotation or the cages in the ends of the casing willV setup circular vibrations therein, and it' the balls in the two cages areon opposite sides otthe shaft the vibrations in one end oif the casingwill be out ot phase with those in the other end, so that the casing asa wiole tends to vibrate about its central part with the i'ree ends otthe casing traveling in patl s ot' minute ainplitude.y rlhe vibrationsso produced are transmitted to the screen cloth by the plates S5,thereby setting up vibrations oit' small amplitude in each particle orthe screen medium. The shatt ot' the vibrator is parallel to the planesor the screen sections so that the vibrations produced are in planesnormal to the plane of the screen and transverse to the direction inwhich tension is applied in the screen. The vertical planes lin whichthe vibrations taire place also contain the paths of travel of the loosematerials passing'downwardly over the screen. The character ot thisvibration is illustrated somewhat diametrically in Fig. 5, which showsan enlarged sectional view or the screen ycloth taken in a planeperpendicular to the airisr of the Vibrator and transversely tothedirection in which tension is applied to the screen. Each particle ofthe screen cloth tends to more in a path 90 slmwn :is substantiallycircular iii siiape. lilith the vibrator located beneath the casing'inthe manner illustrated, the direction ot rotation is preferably in aclockwise direction, as

viewed iii Fig. 3, so that the peripheries ot the rotary elements oit'the vibrator are niovduce an instantaneous or momentary retard-` ationoit the particles ot loose materials passing downwardly over the screen.

.ln practice, the motor, or other driving ineans, which is employed tooperate the yi bratoi, should preferably drive the shati; ata relativelyhigh speed. For example, a-

Aspeed of thirty-.six hundred revolutions per minute has been round togive satisfactory results in the screening crushed ore. The screen clothshould, preferably, be 4under high tension, or in a substantially stili'and rigid condition. l Where relatively coarse screens are used thetension therein may be considerably decreased, or eliminatedaltoget-her, andthe amount or' tension ifor the most satisfactory'vibration ot the screen cloth Will Vary, dependii'ig upon .thecharacter of 'the material being screened, the speed ot vibration,andtl'ienature or vthescreen cloth used. The proper conditions can bestbe determined by trial. `When the parts ot the mechanism are properlyadjusted, the rotation ol' the ifibrator will result in the settinol u ioit liioh ifreui'iencf Vibrations in thev n n l .l

screen cloth. `These Vibrations, although they are minute, are Verypronounced in their effect upon the materials being screened, and.

' l )ueftothc novel coi'istructjion ol" 'the iframe and method oimounting the vibrator, all of the parts olf' the vil 'ating mechanismare llo-` cated beneath 'the screening medium, leaving the upper surfaceoil1 'thescreeii cloth entirely ilrec, as well as the region beneath thescreen at the upper and lower edges thereof. This maires it possible tomount the screening` apparatus conveniently, and tooperate it under allconditions with the highest el'liciei'icy.

i-llthouglil l have shown and described one iorni oi the invention it'orpurposes oit illustration, it Willbe i'inderstood that it may beconstructed in various other embodiments without departing from thescope oit the appeiided claims.

inenibi-rf a horizontal siipporting base membei' ai ged to'connectintegrally said end nienibe and :means it'or piyotally supportingsaidtraine. l

f2. In ricrceiiing apparatus, a supporting traine comprising opstandingparallel end members, a horizontalsupporting base inem- Je' i gsd toconnect integrally said'end incnibei -1 said end members having edgesadapted to support a screen frame, and ineaiis'ifor pivotally supportingsaid frame.

3, lhe combination in screening apparasubstantially parallel end framemem# i single connecting member extending ciitlie central parts ot saidend VVtrame ibers, a screening iiiiedium mounted bei said end .tramemembers, the lateral oite said screening medium being unrtcd andVibrating means mounted on said connecting member and connected toscreening medium to transmit vibra- 'i ons thereto.

et. The combination in screening appara- ,fas olvl an integrally'lornied trame comprisj end walls and a connecting member, a een clothmounted between said end frame members, and vibrating means mounted onsaid connecting member andconnected to sind screen cloth to transmitVibrations` thereto. p n

5. 'llie combination in screeninguppara tus ot parallel end tramemembers,` a single connecting member `extending between the ral parts olsaid end trame members and a i `ne parallel to the plane of said. enditi-aine members, ascreeningl medium mountcd between said end tramemembers, a yibrator mounted on the body portion oi' said connectingmember, and means for operatively connecting said vibrator to saidscreeiiinv in num to transmit vibrations thereto. G. The combinationinscreening apparatus ol an integrally termed supporting tramecomprising upstanding end members anda hoi. intal connecting member, ascreenclotli incurred between said endinembers, and` means tor mountingsaid trame with said screen cloth in an inclined position.

7. he combination in screening apparatus ol" an integrally formedsupporting frame con'iprising opstanding end members and a horizontalconnecting member, a screen clot-h mounted between said end members avibra fing the body portion thereotl located in Slt).

lll() tor, means for mounting said frame With said screen cloth in aninclined position, and

`means for changing' the angular position of insonne endwallssubstantiall;T parallel'to said connectma'v member, and 'a vibratormounted on said connecting member' midwa7 betweeny said end walls andoperatively connected to said -screen cloth, said vibrator andsaidconnccting member' being located beneath said screen cloth.

9. The combination in screening' apparatus of substantially parallel endframe members, a longitudinal frame member extending; between thecentral parts 'of said end frame members, means connected 'to said endframe members for 'iounting' them in an inclined position, a screeningmedium extending tween said end frame members, and a Y' tor mounted onsaid longitudinal member and operatively connected to sai screening'medium on the uncerside thereof.

l0. The combination in screenin(r apparatus of substantiall;7 parallel`end i' e neinbers mounted in an inclined position, a screen lclothmounted in an inclined position between said end frame members, a lonmidinal frame member located beneath said screen cloth and having' theends thereof upturned and connected to said end trame members, a.vibrator mounted on said longjgi- 'tudinal frame member, and atransmitting' Vmember extending upwardl;rv from said vibrator in amembers.' 1 y 11. rllhe combination in screening apparatus ofsubstantially parallel end frame memplane parallel to said end frame`bers mounted in an inclined position, a

screen cloth mounted in an inclined position between said end framemembers, a longitudinal frame member located beneath said screen clothand having the ends thereof upturned and connected to said end framemembers, a vibrator mounted on said lonnitudinal fra-me member, avibrator casina' having),` itsl central part rigidly,7 secured to saidlongitudinal frame member and having the end portions thereof free tovibrate, and' plates secured to tie free end portions of said vibratorcasing;- and extending' upwardly therefrom to engage said screen cloth.

l2'. The combination in screening appara.- tus of sub'stantialljvfvparallel end frame meinbers mounted in an inclined position, a screencloth mounted in an inclined position between said end frame members, alongitudinal frame member located between said screen cloth and having'the ends thereof upturned and connected to said end frame members, a.vibrator mounted on said longitudinal frame member, ay vibrator casinghaving' its central part rigidly secured to said longitudinal framemember and having' the end portions thereof free to vibrate.platessecured to the free end portions of said vibrator casing andextending upwardly7 therefrom to engage said screen cloth, and means insaid vibrator casing for producing substantially. circular' viln'ationsin the free end portions thereof.

rThe combination in screening apparatns ofparallel end frame members. ascreen cloth stretched between said end frame members, a longri'tudine.lframe member connecting said end frame members and located beneath saidscreen cloth. and vibrating' means mounted on said longitudinal'framemembers and operativelyv connected to said screening' cioth forproducing minute circular vibrations therein.

Af. The combination in screening' apparatus of parallel end framemembers. a screen cloth mountechin an inclined position and stretchedbetween said end fram members,

longitudinal frame member extending' beween said cnd frame membersbeneath said `ns ca fied bv said lonnembei' n mi lar vibrations cloth.the .direction of mov said screen ent of each ticle of the screen clothben' toward the edge of the screen cloth when in the .ier part of pathof vibration.

i5. The combination in screening' apparatus of parallel end framemembers. a screen'cloth mounted in an inclined position between said endframe Ymembers, a longitudinal frame member extending' between said endframe members'beneath said screen cloth, means carried by saidlongitudinal frame member for producing' minute circular vibrations insaid screen cloth, the direction of movement of each particle of thescreen cloth being' toward the upper edgre of the screen cloth when inthe upper part of its path of vibration, and means for causing' loosematerials to pass downwardly over said screen cloth.

16. The combination in screening' apparatus of end frame members, ascreen cloth mounted in an inclined position between end frame members,means for causing loose materials to pass downwardl7 over said screencloth transversel;7 to the direction in which tension is applied. alongitudinal frame member extending between said end frame membersbeneath said screen, and vibrating mea-ns mounted on said longitudinalframe member and connected lo said screen cloth for producing' circularvibrations in said screen cloth in planes normal to the plane of the"screen and transverselj.7 to theA direction in which tension isapplied.

17. rl`he combination in screening' apparatus of end frame members, ascreen cloth mounted in an inclined position between end frame members,mea-ns for maintaining' tension in said screen cloth longitudinall7thereof, means for causing loose`V materials to pass downwardly oversaid screen cloth transversely to the direction in which tension isapplied, a longitudinal frame member extending between said end framememproducino' :-1.

llt)

bers beneath said screen, and vibrating means mounted on saidlongitudinal frame fiember and connected in operative engagement withsaid screen cloth for producing circular vibrations in said screen clothinv planes normal to the plane of the screen and transverselyto thedirection in which tension is applied, the direction of movement of eachparticle of the screen cloth in the upper part of its path-oi. vibrationbeing toward the upper part of' said screen cloth.

18. The combination in screening apparatus oit parallel end framemembers, a screen cloth mounted in an inclined position between saidyend frame members and having tension maintained therein in alongitudinal direction, a longitudinal frame member extending betweensaid end frame members beneath said screen cloth, a vibrator casinghaving the central part thereoie` mounted in substantially fixedposition on the central part of said longitudinal 'frame member, saidvibrator casing having free end portions, means comprising unbalancedrotary elements in said end portions forproducing minute circularvib'ations therein, and plates mounted on the free end portions of saidcasing and' extending `upwardly therefrom in planes normal to ythe planeof the screen and transversely to the direction in which tension isapplied in said screen cloth for transmitting said circular vibrationsto said screen cloth;

19. The combination 1n screening apparatus of parallel end framemembers, a

screen clothfmounted in an inclined position between said end framemembers and having tension maintained therein in a longi-` tudinaldirection, a longitudinal frame member extending between said end framemembers beneath said screen cloth, afvbrator casing; having` the centralpart thereoi' mounted in substantially fixed position on the centralpart of .said longitudinal frame member, said vibrator casinghaving freeend portions, means comprising unbalanced l rotary elements in said endportions for In testimony whereof, I have subscribed my name.

BENJAMIN A. MITCHELL.

